Bioinspired Near-Full Transmittance MgF₂ Window for Infrared Detection in Extremely Complex Environments

Abstract

Due to the extreme complexity of the anti-reflective subwavelength structure (ASS) parameters and the drastic limitation of Gaussian beam manufacturing accuracy, it remains a great challenge to manufacture ASS with ultrahigh transmittance on the surface of infrared window materials (such as magnesium fluoride (MgF2)) directly by femtosecond laser. Here, a design, manufacturing, and characterization method that can produce an ultrahigh-performance infrared window by femtosecond laser Bessel beam is proposed. Inspired by the excellent anti-reflective and hydrophobic properties of the special structure of dragonfly wings, a similar structural pattern with grid-distributed truncated cones is designed and optimized for its corresponding parameters to achieve near-full transmittance. The desired submicron structures are successfully fabricated by a Bessel beam after effectively shaping the beam. As a practical application, the bioinspired ASS is manufactured on the surface of MgF2, achieving an ultrahigh transmittance of 99.896% in the broadband of 3–5 μm, ultrawide angle of incidence (over 70% at 75° incidence), and good hydrophobicity with a water contact angle of 99.805°. Results from infrared thermal imaging experiments show that the ultrahigh-transmittance MgF2 window has superior image acquisition and anti-interference performance (3.9–8.6% image contrast enhancement and more accurate image edge recognition) in an environment with multiple interfering factors, which may play a significant role in facilitating applications of infrared thermal imaging technologies in extremely complex environments.

Wide-Size Range and High Robustness Self-Assembly Micropillars for Capturing Microspheres

“…These methods are either costly, complicated and cumbersome steps, or cannot arbitrarily design the structure size and pattern shape, resulting in low controllability and flexibility. A femtosecond laser has the advantages of high resolution, good scalability, and strong controllability, − making it one of the best choices for processing capillary force driven self-assembly microstructures. − For example, Hu et al fabricated self-assembly micropillar structures in photopolymers by femtosecond laser two-photon polymerization (TPP), with a structural height of 2–7 μm, which can capture the diameter of microspheres in 1–4.6 μm and can only capture microspheres with a diameter of less than 5 μm. Subsequently, Ni et al and Hu et al improved the efficiency of TPP technology to manufacture micropillar structures through different shaping optical fields, and its structural height was roughly 2–13 μm, the diameters of the captured microspheres were 5–10 μm, and the capture range was only slightly widened, which was still difficult to meet the requirements for the capture of larger size microspheres in practical applications.…”

Application of Femtosecond Laser Processing Method in the Sustainable Conservation of Stone Cultural Relics: An Example of Green Schist in Wudang Mountain, China

“…In terms of laser-matter interactions, the ultrafast laser-matter interaction usually reflects smaller thermal effects, especially for some non-metallic materials (e.g., quartz composition in the stone materials). Ultrafast lasers are also able to form selective cold ablations, which allow for an overall higher processing quality [28]. In this context, the ultrafast laser processing method is also an alternative use in the preparation of superwetting structures on stone material surfaces [29][30][31].…”

Electrospun Materials with High Reflectance and Polarization Contrast for Sensing Applications in the Mid-Infrared Atmospheric Window

“…The development of remote sensors is complex because of the multiple constraints for service in expansive and challenging field environments. − Ding et al have underlined the drastic reduction in detection efficiency of conventional IR thermal imaging systems when the targeted objects are embedded in isothermal scenes and shadowed areas, due to poor image edge recognition and major loss of contrast, respectively, and have successfully alleviated these issues by developing an ultrahigh-transmittance IR window surfaced with antireflective subwavelength structures for their optical setup . Significant efforts are also dedicated to developing hyperspectral polarimetric electro-optic IR sensors that simultaneously gather information on the chemical nature of the targeted objects and on the state of polarization of their optical response. − This ability also improves detection efficiency under these challenging conditions or when the targets possess a chemical composition similar to their surroundings, thereby helping to reduce the rate of false positives or false negatives. , For instance, it can facilitate the detection of gaseous or liquid contaminants by revealing a reduction in polarization contrast resulting from their nonpolarized MIR response.…”